Method for assessing the deterioration of motor oil

ABSTRACT

A method for assessing the deterioration of motor oil is presented, in which the oil viscosity of the motor oil is measured by a sensor, and the length of an oil-change interval is determined in an evaluating electronics having a display device. According to the invention, it is provided that a temperature sensor for the simultaneous determination of the oil temperature is assigned to the sensor for measuring the oil viscosity, and the oil viscosity and oil temperature are measured in the cooling phase of the engine after it has been switched off.

[0001] The present invention relates to a method for assessing the deterioration of motor oil, having the features cited in the preamble of claim 1.

BACKGROUND INFORMATION

[0002] Software-based systems are known for indicating the necessity of an oil change in motor vehicles, some of which are based on algorithms, which evaluate parameters such as the kilometers driven since the last oil change or the frequency of cold starts.

[0003] Alternatively, in other known methods, recourse is had to sensor signals, which directly describe the physical condition of the oil, it being possible using appropriate sensors to measure, for example, the dielectric constant of the oil or, as a far more reliable variable, the oil viscosity. In this context, it is possible to derive a viscosity-based oil-change criterion from the determination of the viscosity change in the motor oil since the last oil change, because motor oil deterioration is usually associated with an increase in the viscosity value. In an evaluating electronics having an associated display device, it is possible in conventional systems to store, for example, a viscosity threshold value, which is compared with the measured viscosity values of the motor oil, an indication being provided to the vehicle driver regarding the impending necessity for the next oil change when the viscosity threshold value is exceeded.

[0004] The physical oil parameters that are measured using these methods that are known from the related art are generally temperature-dependent, so that, to determine a comparison value, a temperature-compensation calculation is necessary.

[0005] In addition, in conventional methods for determining the oil viscosity, the problem remains that, because the engine is in operation, a large part of the oil medium to be measured is in circulation, so that it can happen that it is not always possible to sufficiently wet the oil-viscosity measuring sensor, thus resulting in measuring errors in the measurements that are carried out.

ADVANTAGES OF THE INVENTION

[0006] In contrast to the methods known from the related art for measuring the oil viscosity and the resulting assessment of the deterioration of the motor oil, the method according to the present invention having the features cited in the characterizing part of claim 1 has the advantage that, as a result of the simultaneous determination of the oil temperature using a temperature sensor that is assigned to the sensor for measuring the oil viscosity, it is possible to reliably record a viscosity-temperature characteristic curve, a further precise evaluation variable being available for evaluating the oil condition using the viscosity index that is characterized by the temperature-viscosity curve. In addition, the method according to the present invention, as a result of measuring the oil viscosity and the oil temperature in the cooling phase of the engine after it has been switched off, has the advantage that the measurements can be carried out within a relatively large temperature range (assuming ambient temperatures in the area of 25° C. and operating temperatures of the motor oil in a range of up to 150° C.). Of course, a measuring temperature range of this type is also given during the warm-up phase of the motor oil, although the above-mentioned disadvantages such as insufficient wetting of the measuring censor(s) can occur as a consequence of the motor being in operation.

[0007] The control of the oil-temperature and oil-viscosity measurements as well as the storing and evaluating of the measuring results obtained can be accomplished according to the present invention by a engine control unit assigned to the engine. This offers the advantage that, for carrying out the method according to the present invention, no special control electronics is necessary, because conventional engine control units are still in operation even during a so-called slowing-down time after the engine is switched off. This slowing-down time can be up to 30 minutes, so that it is advantageous to carry out the measurements of oil temperature and oil viscosity in a time interval of up to 100 minutes, preferably from 10 to 30 minutes after the switching-off of the engine. In this way, numerous measuring values are produced, which make possible a sufficiently precise viscosity-temperature characteristic curve for the assessment of the deterioration of the motor oil.

[0008] It can also be expedient to assign the evaluation to a computing device that is arranged in the instrument panel, thus resulting in a further reduction in the necessary components. Alternatively, it is also, of course, conceivable to integrate the evaluation in the engine control unit. Because the oil-viscosity and oil-temperature measuring values are determined and their subsequent evaluation is carried out after the engine has been turned off, sufficient computing capacity is present for the evaluation of the measuring values, in contrast to evaluation times while the engine is in operation. In response to the next commencement of travel, the measuring values obtained can be conveyed to the vehicle user by the display device assigned to the evaluating electronics. Because the condition of the motor oil during a single journey changes only very slightly, conveying oil-condition information outside of “real-time operation” is unproblematic.

DESCRIPTION OF THE METHOD ACCORDING TO THE PRESENT INVENTION

[0009] After the engine of a motor vehicle is switched off, the measuring cycle necessary for the method according to the present invention for the simultaneous determination of the oil-temperature and the oil-viscosity values is set in motion by the engine control unit arranged on the engine. In the cooling phase of the engine, a continuous measurement of the relevant variables is carried out in fixed time intervals or as a function of a specifiable temperature interval of the motor oil.

[0010] For example, it is conceivable to carry out the determination of the oil-viscosity values in response to a cooling-off of the motor oil by 5° C. The overall interval for the continuous determination of oil temperature and oil viscosity basically corresponds to the slowing-down time of the engine control unit. During this slowing-down time, the oil-temperature/oil-viscosity values measured are simultaneously stored in an evaluating electronics, and a viscosity index, as the determinative variable for assessing the motor oil deterioration, is formed from the corresponding characteristic curve.

[0011] If, in the context of the evaluation of the recorded values, it is determined that the deterioration of the motor oil has progressed to the point that a change in motor oil is necessary, then in response to the next engine start, this information is conveyed to the vehicle user by an appropriate display device.

[0012] Of course, in the cooling phase of the engine during the slowing-down time of the engine control unit, it is also possible to record and evaluate measuring values regarding other fluids that are present in the vehicle. 

What is claimed is:
 1. A method for assessing the deterioration of motor oil, in which the oil viscosity of the motor oil is measured by a sensor and the length of an oil-change interval is determined in an evaluating electronics having a display device, wherein a temperature sensor for the simultaneous determination of the oil temperature is assigned to the sensor for measuring the oil viscosity, and the oil viscosity and oil temperature are measured in the cooling phase of the engine after it has been switched off.
 2. The method for assessing the deterioration of motor oil as recited in claim 1, wherein the oil-temperature and oil-viscosity measurement as well as the evaluation are regulated and monitored by an engine control device that is assigned to the engine.
 3. The method for assessing the deterioration of motor oil as recited in one of claims 1 or 2, wherein the measurement of the oil temperature and oil viscosity takes place in a time interval of 10 to 100 minutes after the engine has been switched off.
 4. The method for assessing the deterioration of motor oil as recited in one of claims 1 through 3, wherein the evaluation is assigned to a computing device that is arranged in the instrument panel, the computing device being driven and monitored by the engine control unit. 